Recently, the coloring method for a solid-state imaging device in primary use comprises an on-chip color filter structure, in which a color filter layer is formed directly on the surface of a semiconductor substrate provided with a solid-state imaging element. This method has taken the place of a filter adhesion system, in which a glass plate on which is disposed a color filter layer is adhered on a solid-state imaging element. Furthermore, a compact-size solid-state imaging device has a microlens formed on top of the color filter layer to converge incident light to a photodiode part for improving photosensitivity.
In the following, a conventional solid-state imaging device will be explained.
FIG. 5 is a cross-sectional view showing an image pick-up part of a conventional solid-state imaging device. In FIG. 5, reference numeral 13 represents a n-type semiconductor substrate provided with a solid-state imaging element; 12 represents a p-well layer; 11 represents a photodiode part; 10 represents a charge transfer part; 9 represents a silicon oxide or nitride film; 8 represents a polysilicon electrode; 14 represents a photo-shielding metal layer; 5 represents a surface protective coating of a semiconductor element; 19 represents a planarization layer for flattening an element; 4 represents a color filter layer; 3 represents an intermediate transparent film; and 1 represents a microlens. Furthermore, another conventional example comprises one additional layer of metal film formed via a silicon oxide film on the photo-shielding metal layer 14 for strengthening the photo-shielding and forming a semiconductor element with the surface protective coating 5. In this way, the microlens 1 is adjusted and positioned to each photodiode part, and light converged by the lens is directed to the photodiode part 11 to enhance sensitivity. Among electrons and holes arising from photoenergy in the photodiode part 11, the electrons are forwarded to the charge transfer part 10 by voltage applied to the polysilicon electrode 8. The transferred electrons are then forwarded to an output part by potential energy created in the charge transfer part 10 through the voltage applied to the polysilicone electrode 8.
Another example, which is disclosed in Laid-open Japanese patent application No. (Tokkai Hei) 5-134111, is an invention which controls an optical path by forming the intermediate film 3 disposed under the microlens 1 using a material such as polyimide whose refractive index is larger than the refractive index of the microlens.
Also, the color filter 4 is not used in a three chips imaging device for video cameras or in a black-and-white CCD.
However, the above-mentioned conventional configuration had the problems as follows, which resulted in difficulty in improving sensitivity.
In general, a solid-state imaging device is placed where light is converged by an optical lens and an image is formed. In this case, the incident angle varies according to a diaphragm size of an opening part. In particular, when a diaphragm is in an open state, as shown in FIG. 4, the optical path of a light beam 18 entering obliquely does not reach a photodiode part 11, but instead is directed to a photo-shielding film 7. As a result, the sensitivity does not improve as expected when the diaphragm of an optical lens is open.
Furthermore, in order to direct as many oblique photocomponents to a photodiode part as possible, it is known to shorten the distance from the microlens 1 to the photodiode part 11 (hereinafter abbreviated as a photodiode part distance). In the conventional system, however, aluminum is used for the photo-shielding film 14, and since this photo-shielding film 14 is shared also as surrounding wirings, a thickness close to 1 .mu.m is needed. In addition, a stepwise difference at the opening part becomes large, so that it is necessary to form the planarization layer 19 sufficiently in order to form the color filter and the microlens uniformly. Also, another example of the solid-state imaging device which applies the method of forming two stages of photo-shielding layers cannot shorten the photodiode part distance due to the same reason mentioned above.
In addition, the Laid-open Japanese patent application No. 5-134111 proposed to provide a lens effect exceeding the refractive index 1.56 of the microlens, but as the refractive index increases, the light transmittance of the material deteriorates. As a result, the material is colored, which leads to deterioration of the sensitivity.